Studies were completed on the opsonic and bactericidal activity of a monoclonal antibody directed against the outer membrane proteolipid, H.8, of Neisseria gonorrhoeae. In addition to its anti-gonococcal and opsonic activity described in earlier reports, it was found to override the regulatory function of the serum glycoprotein C1 inhibitor and to allow activation of C1 with sequential activation of the classical complement pathway. Despite early suggestions that Neisseria gonorrhoeae directly activated the classical complement pathway, meticulous studies prohibiting spontaneous activation of C1 by autocatalytic mechanisms proved otherwise. Qualitative measurement of state of activation of C1s proved that Neisseria gonorrhoeae dose not directly activate the classical complement pathway in the absence of antibody whether or not C1 inhibitor is present. When antibodies are included in the assay, activation always occurs.